FS_POSAB/IOF_POSA & FS_POSRE/IOF_POSR
These traps position the file pointer.
| Trap | Value in D0.B | Action |
|---|---|---|
| FS_POSAB/IOF_POSA | $42 | Position file absolute |
| FS_POSRE/IOF_POSR | $43 | Position file relative |
| Call Parameters | Return Parameters | ||
|---|---|---|---|
| D0.B | See above | D0.L | Error return. |
| D1.L | File position | D1.L | New file position. |
| D3.W | Timeout | D3.L | Preserved. |
| A0.L | Channel ID | A0.L | Preserved. |
| A1.L | A1.L | Corrupted. | |
Errors
| ERR_NC | Not complete. |
| ERR_NO | Channel not open. |
| ERR_EF | End of file. |
Notes
- All registers not shown above are not used on entry and are preserved on exit.
- The value in D1.L is the absolute position requested for FS_POSAB/IOF_POSA and is the offset from the current position for FS_POSRE/IOF_POSR.
- If either trap returns with an off limits error then the pointer is set to the nearest limit (either 0 or the end of the file).
- By setting D1 to 0 and using FS_POSRE/IOF_POSR the current position of the file can be determined.
- In the case of FS_POSAB/IOF_POSA if the call is made for a direct sector access channel a special file position flag can be specified in D1. Using $F0FFF0FF returns the sector offset of the first physical sector of the current partition on multiple-partition devices (SMSQ v2.77+), otherwise D1 is unchanged.
Example
The example below shows the use of FS_POSRE/IOF_POSR to find the current position in the file. It is assumed that A0 contains the channel ID.
pos moveq #fs_posre,d0 ; $43
moveq #0,d1 ; To find the current position
moveq #-1,d3 ; Timeout
trap #3 ; The current position is now in D1.L
tst.l d0 ; OK? . .
bne error ; . . no!
george.gwilt